1. Field of the Invention
The present invention relates to a method of making a high resolution, lead to shield short-resistant magnetic head, and, more particularly, to a read head with a very small read gap for high resolution and insulation layers that are substantially aligned with first and second leads for preventing shorting of the leads to first and second shield layers.
2. Description of Related Art
An MR read head includes an MR sensor positioned between first and second non-magnetic gap layers which, in turn, are positioned between first and second shield layers. The resistance of the MR sensor changes in response to magnetic fields on circular tracks of a rotating disk. A sense current conducted through the MR sensor results in voltage changes that are detected by processing circuitry as readback signals. The MR sensor may be an anisotropic MR (AMR) sensor, or a spin valve sensor.
A spin valve sensor includes a spacer layer, positioned between a pinned layer and a free layer. First and second lead layers are connected to side edges of the spin valve sensor for conducting a sense current therethrough. The magnetization of the pinned layer is pinned at 90.degree. to the magnetization of the free layer, and the magnetization of the free layer is free to respond to magnetic fields from the rotating disk. The magnetization of the pinned layer is typically pinned by exchange coupling with an antiferromagnetic layer. A spin valve sensor is characterized by a magnetoresistive (MR) coefficient that is substantially higher than the MR coefficient of an anisotropic magnetoresistive (AMR) sensor. For this reason a spin valve sensor is sometimes referred to as a giant magnetoresistive (GMR) sensor.
Each lead layer has an end edge that may abut a respective side edge of the MR sensor to form what is known in the art as a contiguous junction. The distance between contiguous junctions in an MR read head defines the track width of the head. A hard magnetic layer typically underlies each lead layer and includes an end edge that abuts a respective side edge of the MR sensor. The hard magnetic layer, also known as a hard bias layer, longitudinally biases the MR sensor, stabilizing its magnetic domains to prevent Barkhousen noise. In another type of junction, each lead layer and bias layer overlap a portion of the MR sensor, forming a continuous junction. The track width of an MR read head with continuous junctions is defined by the distance between the overlapping portions. The contiguous junction configuration is preferred to the continuous junction configuration because one masking step can be employed for defining the track width of the MR sensor, as well as for depositing the bias layer and leads that form the contiguous junctions.
The areal or bit density of an MR read head is determined by its track width and read gap. Track width defines the tracks per inch of recording medium (track density) and the read gap defines the bits per inch along a track (linear density). From these parameters the bits able to be read per square inch of recording medium can be determined. In the construction of an MR read head, it is easier to increase track density than linear density. In order to maximize linear density, the first and second gap layers at the top and the bottom of the MR sensor must be extremely thin. For instance, for a 10 Gb/in.sup.2 spin valve read head, the total read gap should be about 150 nm. With an MR structure thickness of about 35 nm this leaves about 115 nm to be divided between the first and second gap layers. Such gap layers are not sufficiently thick to protect the lead layers from electrical shorts. Because of the large area of the lead layers there is a high risk that the gap layers will have pin holes that permit shorting to the first and second shield layers. This has a serious impact on manufacturing yield.
One way to minimize shorts is to deposit additional insulation material outside the sensor frame. This can be accomplished by depositing a layer of insulation immediately on top of the first gap layer, outside the sensor frame, and depositing another layer of insulation, outside the sensor frame, just before the second gap layer is formed. This leaves only the first and second gap layers within the sensor frame, but thickens up the insulation outside the sensor frame where the lead layers extend to the terminals. Unfortunately, a portion of each lead layer between the contiguous junction and the additional insulation layers is protected only by the first and second gap layers, which leaves that portion at risk of shorting to a shield layer. Another problem with this arrangement is that the additional insulation layers thermally insulate the MR sensor, thereby increasing the risk that heating of the MR sensor will alter magnetic moments of its magnetized layers. Still another problem is that a masking step is required for each of the two additional insulation layers. Each masking step requires that a vacuum be broken in a deposition chamber so that a wafer with rows and columns of heads can be removed for masking. Photoresist is spun on the wafer, exposed with light having a desired pattern, and then developed to remove the exposed portion or portions where material is to be deposited. Each time the wafer is taken out of the deposition chamber, the exposed surfaces of any metallic layers are oxidized which lessens the adherence between metallic and insulation layers.
In addition to the two masking steps required for the two insulation layers, at least three additional masking steps are required to construct the MR sensor and the leads. After the first masking step, a second masking step is required to define the side edges of the MR sensor and a first lead layer film portion of each lead layer. A third masking step is then employed to define the height of the MR sensor by removing all MR sensor material not removed by the second masking step. A fourth masking step is then employed to deposit a second lead layer film portion for each lead layer that is electrically connected to and extends from the first lead layer film portion to one of the terminals. A fifth masking step is then employed for depositing the second insulation layer discussed hereinabove. With this arrangement five masking steps are required to complete just the MR sensor and the insulation layers.